''There was a 20% reduction in lung cancer mortality when you compared CT to X-ray," says Constantine Gatsonis, PhD, a lead statistician in the analysis for the study and a professor of biostatistics at Brown University in Providence, R.I.

Sponsored by the National Cancer Institute, the National Lung Screening Trial (NLST) was halted early after the trial's independent Data and Safety Monitoring Board notified the NCI that the data accumulating made it clear that the CT technology for lung cancer screening was superior to the standard X-ray in reducing deaths from lung cancer.

A letter dated Nov. 4 was sent to inform the more than 53,000 trial participants, all current or former heavy smokers aged 55 to 74, of the results.

“I would classify it as moderate,” Christine Berg, MD, NLST, project officer for the Lung Screening Study at NCI, says of the 20% reduction.

Even so, she tells WebMD, medical organizations that issue screening guidelines are expected to “take this information very seriously.”

Currently, she says, no major medical organizations that typically suggest screening guidelines for primary health care providers have issued recommendations for heavy smokers who don’t have symptoms of lung cancer.

More than 222,000 people in the U.S. are expected to be diagnosed with lung cancer and cancer of the bronchus this year, according to the NCI, with 157,300 deaths expected.

More than 94 million current and former smokers in the U.S. are at high risk for lung cancer, the NCI says.

Lung Cancer Screening: Trial Details

Chest X-ray and low-dose helical CT scans (also called spiral CT) have both been used to find lung cancer early. But in the NLST, investigators were looking at which way of detecting lung cancer reduced death rates more.

The trial, launched in 2002, examined more than 53,000 former or current heavy smokers who had a history of at least 30 ''pack-years" but no symptoms or signs of lung cancer when they entered the trial.

Pack-years are computed by multiplying the average number of packs of cigarettes smoked per day by the number of years a person has smoked. A person who smokes a pack a day for 30 years, for instance, or 2 packs for 15 years, has a 30 pack-year history.

Participants were assigned randomly to either a low-dose helical CT or standard chest X-ray group and were given the same test annually for three years.

Lung Cancer Screening: Trial Results

When the researchers analyzed the results to date in late October, they found that the benefit of CT scans was clear.

The 20% reduction with CT scans is termed “very important," by Gastonis.

''What we are showing is, heavy smokers can see a benefit here [with CT screening] in mortality," he says.

According to the NCI, for every 300 participants screened with low-dose helical CT, one life has been extended.

A surprise finding is that the CT screening group also had a 7% reduction in overall death rate from any cause compared to the chest X-ray group, he says.

The ''false-positive" rate -- those screenings that detected an abnormality that upon further evaluation was not lung cancer -- was about 25% in the trial, Gatsonis says. In other studies of lung cancer CT screenings, the rate of abnormalities shown in former and current smokers ranged from 20% to 60%, with most of the abnormalities not turning out to be lung cancer.

The false positives, experts say, can cause anxiety and tests such as biopsies that could turn out to be negative.

But finding the cancer early with screening can extend life.

Screening for Lung Cancer: Perspective

The reduction found with CT scans over standard X-rays is very good, says Regina Vidaver, PhD, executive director of the National Lung Cancer Partnership, a nonprofit organization devoted to research and education.

"Having a 20% decrease in mortality from screening is outstanding," she tells WebMD. She was not involved in the study but reviewed the findings for WebMD.

She points out, however, that the study included only heavy smokers and that one in four is ''a very high false-positive rate."

Screening for Lung Cancer: Practical Matters

Reimbursement for a lung low-dose helical CT scan, used as it was in the trial as a screening test before any symptoms or signs arise, is not provided by most insurance carriers, according to the NCI.

The estimated Medicare reimbursement for a diagnostic CT of the lung when lung cancer is suspected is about $300, the NCI says.

The study results are expected to provide valuable information to help experts make recommendations for screening, Gatsonis says.

The machines to perform low-dose helical CT scans are widely available at hospitals and free-standing radiology clinics in the U.S., according to the NCI. In the test, X-rays scan the entire chest in about 15 seconds, with the scanner rotating around the person as he lies still on a table. Images from the X-ray data are fed to a computer, and two-dimensional pictures of the lungs with great detail are produced.

Berg has this advice: “I would personally recommend that a heavy smoker with no signs or symptoms of lung cancer go talk to their physician and discuss the findings released today.” A decision about cancer screening should be based on medical history and other factors, she says.